PROJECT SUMMARY This proposal focuses on targeting neoantigens in malignant brain tumors in well defined orthotopic, syngeneic preclinical models, understanding how type 1 conventional dendritic cells (cDC1) prime neoantigens, and how immune responses to neoantigens develop in newly diagnosed glioblastoma (GBM) patients enrolled in a novel clinical trial combining personalized vaccination with checkpoint blockade. GBM remains a lethal cancer and carries a median survival of 15 months with standard-of-care treatments, highlighting a clear need for more effective treatments. The application of genomics to immunotherapeutic approaches is an exciting area of investigation in many cancer types, and this proposal employs this methodology. This nexus, termed ?cancer immunogenomics?, is used to identify tumor-specific somatic mutations that may be processed and presented on major histocompatibility molecules. These ?neoantigens? can be recognized by the immune system and form the basis for anti-tumor immune responses. We have applied the cancer immunogenomics approach to the study of GBM both in preclinical models as well as in a novel personalized immuno-oncology cancer vaccine program for GBM patients. However, in order to fully exploit the potential of targeting neoantigens in GBM, further work is needed to understand whether targeting multiple neoantigen targets using polyvalent vaccines can improve tumor control and how neoantigens are presented to the immune system in brain cancers. How antigen is presented in the central nervous system remains unclear, and understanding the immunobiology of this process is inextricably linked to effective neoantigen targeting. In parallel, it is critical to determine how anti-tumor immunity is amplified in patients treated with personalized cancer vaccines in combination with immunopotentiating checkpoint blockade therapies. To this end, we are applying cancer immunogenomics preclinically and translationally to address these key questions. In Aim 1, we will determine the effectiveness of polyvlalent neoantigen vaccination targeting MHC class and and/or MHC class II neoantigens on survival and the immunologic effects of these vaccines on the brain tumor microenvironment. In Aim 2, we will test the hypothesis that cDC1 present neoantigen in vivo and can augment the efficacy of neoantigen-targeting vaccines. We will also further characterize the anatomic location of this critical cell population during the anti-tumor immune response. In Aim 3, we will perform correlative analysis of a novel clinical trial we are conducting to determine whether checkpoint blockade agents augment the immune responses generated with personalized vaccines and whether the genomes of recurrent tumors that progress on this trial are remodeled and/or show evidence of neoantigen specific cancer immunoediting. Together, these Aims will provide new insights into an immunogenomics-centered approach to treating GBM as well as the immunobiology of neoantigen presenation and T cell specific immune priming that has clear and imperative clinical implications.